What is the QTc Interval?

The QTc interval is the corrected QT interval, which represents the time it takes for the ventricles of the heart to depolarize and repolarize. Because the raw QT interval varies based on the heart rate (shortening as heart rate increases and lengthening as it decreases), clinicians use various mathematical formulas to "correct" the value. This allows for a standardized assessment of the patient's cardiac health, regardless of their current heart rate.

How to Use This QTc Calculator

To use this professional medical tool, follow these steps:

1. Obtain the QT interval (in milliseconds) from an electrocardiogram (ECG/EKG).
2. Note the patient's current heart rate in beats per minute (BPM).
3. Select your preferred calculation method (Bazett is common, though Fridericia is often preferred for high or low heart rates).
4. Click "Calculate" to see the result.

Understanding the Formulas

Several formulas exist to calculate QTc. The Bazett formula (QTc = QT / √RR) is the most widely used in clinical practice, though it tends to over-correct at high heart rates. The Fridericia formula (QTc = QT / RR^(1/3)) is often considered more accurate for patients with tachycardia or bradycardia. Our tool also supports the Framingham and Hodges equations for comprehensive clinical analysis.

Normal QTc Ranges

While interpretations should always be performed by a qualified medical professional, typical normal QTc values are generally considered to be below 440ms for men and 460ms for women. A QTc interval longer than 500ms is associated with an increased risk of developing dangerous arrhythmias like Torsades de Pointes.